Spectroscopic imaging combines digital imaging and molecular spectroscopy techniques, which can include Raman scattering, fluorescence, photoluminescence, ultraviolet, visible and infrared absorption spectroscopies. When applied to the chemical analysis of materials, spectroscopic imaging is commonly referred to as chemical imaging. Instruments for performing spectroscopic (i.e. chemical) imaging typically comprise image gathering optics, focal plane array imaging detectors and imaging spectrometers.
In general, the sample size determines the choice of image gathering optic. For example, a microscope is typically employed for the analysis of sub micron to millimeter spatial dimension samples. For larger objects, in the range of millimeter to meter dimensions, macro lens optics are appropriate. For samples located within relatively inaccessible environments, flexible fiberscopes or rigid borescopes can be employed. For very large scale objects, such as planetary objects, telescopes are appropriate image gathering optics.
For detection of images formed by the various optical systems, two-dimensional, imaging focal plane array (FPA) detectors are typically employed. The choice of FPA detector is governed by the spectroscopic technique employed to characterize the sample of interest. For example, silicon (Si) charge-coupled device (CCD) detectors or CMOS detectors are typically employed with visible wavelength fluorescence and Raman spectroscopic imaging systems, while indium gallium arsenide (InGaAs) FPA detectors are typically employed with near-infrared spectroscopic imaging systems.
Spectroscopic imaging can be implemented by one of several methods. First, dispersive point or line illumination spectrometer can be raster-scanned over the sample area to create a map of the spectroscopic content. Second, spectra can be collected over the entire area simultaneously, using an active optical imaging filter such as AOTF or LCTF. Here the materials in these optical filters are actively aligned by applied voltages or acoustic fields to produce the desired bandpass and transmission function.
Raster scanning the sample with a dispersive spectrometer having a stable transmission is rather time consuming. The second approach, while providing a more expeditious scanning method, can introduce inaccuracies caused by temperature variation and device-specific characteristics. Any inconsistency in the material and its orientation over the optical surface will modify the transmission function both spatially and over time. Accordingly, there is a need for a method and apparatus for super montage rapid imaging system to provide spectroscopic image of a large area.